there are many types of pop ups such as renewal pop-ups, alerts and notification pop ups, threat detection pop ups etc. Stopping these pop ups may result in trouble instead you should try to limit or change alerts settings.
if the mcafee subscription is expired then you should know how to stop mcafee pop ups using the method provided in link.
the reason you get pop ups from Mcafee even after uninstalling Mcafee is web extension and leftover files. when the program is removed but has certain leftover files or web extensions it might affect the web browser or system and in result it may give our annoying pop ups.
hope this helps your Question.